It is often desirable to adjust the composition of an available gas mixture to obtain a mixed product gas blend desired for a particular use. While the desired gas composition can more or less often be produced by separating individual components of an available gas mixture and remixing these separated components in desired proportions, such procedure is not always easily or successfully practicable using the conventional chemical unit operations. Furthermore, the economics of such approach may be impractical.
Selective adsorption of one or more components of an available gas mixture has been advocated in certain instances in attempts to achieve the state goal, U.S. Pat. No. 3,720,042, for example, is directed to a PSA process for recovering from a starting mixed gas comprising these, (1) a pure hydrogen product and (2) a mixed stream comprised of hydrogen and carbon monoxide in definite proportions. The patent method involves selective adsoprtion of carbon monoxide from the feed gas to provide pure hydrogen as the collected primary effluent. The sorbed CO fraction is then recovered by vacuum desorption and mixed with untreated starting gas mixture to provide the mixed stream of desired H.sub.2 /CO molar ratio.
In U.S. Pat. No. 4,077,779, of applicant and another inventor PSA systems and methods are described applicable to bulk separation of hydrogen from a mixed gas also containing CO.sub.2 and/or CH.sub.4. The disclosed separation is carried out an in an arrangement of 4, 5 or 6 parallel adsorbent beds, each undergoing a sequence of operations: (a) adsorption of components from the mixed gas feed while recovering unadsorbed hydrogen; (b) rinsing the sorbate-laden bed with a recompressed stream of secondary gas (CO.sub.2), then (c) gas withdrawal to reduce bed pressure to an intermediate level, followed by (d) purging with extraneous gas, (e) evacuation to subatmospheric pressure level and (f) repressuring to superatmospheric level by recycle of hydrogen.